ASSM bitmap freelists Oracle Database Tips by Donald Burleson

Oracle Grid Computing with RAC

Automatic Segment Space Management

When an object such as a table or index is created using the locally managed tablespace, with automatic segment-space management enabled, there is no need to specify the pctfree or freelists.

The in-segment free/used space is tracked using bitmaps as opposed to the free lists. When you cannot use the locally managed tablespace, and therefore the automatic management space feature, you have to depend on the traditional method of managing free lists and free lists groups. We will cover the free list method of RAC in a later part of this section.

Automatic segment-space management offers the following benefits:

• It provides administrative ease of use by avoiding the specification of storage parameters.
   

• It is a good method for handling objects with varying row sizes.
   

• It provides better run-time adjustment for variations in concurrent access and avoids tedious tuning methods.
   

• It provides better multi-instance behavior in terms of performance/space utilization.

However, note that this automatic feature of segment space management is available only with locally managed tablespaces and their objects. A new column called SEGMENT_SPACE_MANAGEMENT AUTO has been added to the dba_tablespaces view to indicate the segment space management mode used by a tablespace.